The present invention relates generally to a process for recovering copper from a copper-containing ore, concentrate, or other copper-bearing material, and more specifically, to a process for producing cathode copper without the use of solvent/solution extraction, ion exchange of copper, or related processes to refine and concentrate the copper-bearing solution.
Hydrometallurgical treatment of copper containing materials, such as copper ores, concentrates, and other copper-bearing materials, has been well established for many years. Currently, there exist many creative approaches to the hydrometallurgical treatment of these materials; however, common to almost all of the processes either now known or under development is the use of solvent extraction and electrowinning (SX-EW) for solution purification and copper recovery. Although SX-EW is not without its drawbacks, the proven success in the copper SX-EW field has made this approach standard for production of high quality copper products.
The traditional hydrometallurgical process for copper recovery involves first leaching copper-containing material with an acidic solution, either atmospherically or under conditions of elevated temperature and pressure. The resultant process streamxe2x80x94the so-called pregnant leach solutionxe2x80x94is recovered, and in a solvent extraction (or solution extraction, as it is sometimes called) stage, is mixed with an organic solvent (i.e., an extractant), which selectively removes the copper from the pregnant leach solution. The copper-loaded extractant is then mixed with an aqueous acid solution, which strips the copper from the extractant, producing a solution stream suitable for electrowinning. This resultant solution stream is highly concentrated and relatively pure, and typically is processed into high quality copper cathode in an electrowinning circuit.
In general, electrowinning of copper consists of the electrolytic deposition (sometimes called xe2x80x9cplatingxe2x80x9d) of copper onto a cathode and the evolution of oxygen at an anode. In a simple design of an exemplary electrowinning unit, a set of cathodes and anodes are set in a reaction chamber containing the copper-containing electrolyte. When the unit is energized, copper ions are reduced onto the cathode (i.e., plated). Plating of copper typically occurs on copper starter sheets or stainless steel blanks. Anodes are quasi-inert in the electrolyte and provide a surface for oxygen evolution. The copper plates produced by the electrowinning unit can be in excess of 99.99 percent pure.
Purification of copper from the pregnant leach solution by solvent extraction has proven to be a successful means of providing a concentrated copper solution suitable for electrowinning of highly pure copper metal. Direct electrowinning of copperxe2x80x94that is, plating of copper directly from the pregnant leach solution without the intervening step of purification by solvent extractionxe2x80x94is known. However, the copper recovered by such so-called direct electrowinning processes often is too impure for sale or use as is, and thus, generally must be further refined at an additional cost, or may be sold at a discount. More specifically, prior art techniques have shown the ability for direct electrowinning of copper to produce a relatively low-quality copper product.
An effective and efficient method to recover copper from copper-containing materials, especially copper from copper sulfides such as chalcopyrite and chalcocite, that enables high copper recovery to be achieved at a reduced cost over conventional processing techniques would be advantageous.
While the way in which the present invention addresses the deficiencies and disadvantages of the prior art is described in greater detail hereinbelow, in general, according to various aspects of the present invention, a process for recovering copper and other metal values from a copper-containing material includes obtaining a copper-containing solution from, for example, a pressure leaching system, and then appropriately conditioning the copper-containing solution for electrowinning. In a preferred aspect of the invention, the composition of the copper-containing solution is similar to the composition of the electrolyte produced by a solvent extraction circuit, for example, with respect to acid and copper concentrations. In accordance with the various embodiments of the present invention, however, the copper-containing solution is not subjected to solvent extraction.
In accordance with an exemplary embodiment of the present invention, a process for recovering copper from a copper-containing material generally includes the steps of: (i) providing a feed stream containing copper-containing material; (ii) subjecting the copper-containing feed stream to atmospheric leaching or pressure leaching to yield a copper-containing solution; (iii) conditioning the copper-containing solution through one or more chemical or physical conditioning steps; and (iv) electrowinning copper directly from the copper-containing solution, without subjecting the copper-containing solution to solvent extraction. As used herein, the term xe2x80x9cpressure leachingxe2x80x9d shall refer to a metal recovery process in which material is contacted with an acidic solution and oxygen under conditions of elevated temperature and pressure.
In one aspect of a preferred embodiment of the invention, one or more processing steps are used in order to separate copper from the acid in a recycled portion of the lean electrolyte from the direct electrowinning process, thus enabling the rejection of a portion of the acid component from the process circuit without rejecting a significant portion the copper. As discussed in greater detail hereinbelow, a number of conventional or hereafter devised processes may be utilized to separate copper from acid in the feed stream. For example, in accordance with one aspect of an exemplary embodiment of the invention, a copper precipitation step may be utilized to precipitate solubilized copper from a lean electrolyte stream onto the surfaces of solid particles in a copper-containing material stream in advance of the pressure leaching step, thus separating the copper from the acid solution.
In an aspect of another embodiment of the invention, a recycle circuit is used intermediate to the leaching and electrowinning steps to facilitate control of the composition of copper-containing solution entering the electrowinning stage, and to thus enhance the quality of the copper recovered therefrom.
In accordance with various preferred aspects of the present invention, by providing for the electrowinning of copper directly from a copper-containing solution without first subjecting the copper-containing solution to solvent extraction, the present invention enables lower-cost recovery of copper and eliminates the expenses associated with solvent extraction, such as specialized reagents, process apparatus and equipment, and energy resources. Furthermore, in accordance with one preferred aspect of the invention, careful control of the composition of the copper-containing solution entering the electrowinning circuit enables production of high quality, uniformly-plated cathode copper.
These and other advantages of a process according to various aspects of the present invention will be apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.